1. Field of the Invention
The present invention relates generally to filtration apparatus for removing suspended solids in a liquid or gas stream, and more particularly relates to a new and improved tube-type filter element for use in such apparatus.
2. Description of the Prior Art
Tube-type filters for use in purifying fluids ordinarily found in industrial applications typically include a vertically mounted tank having a lower inlet port and an upper outlet port with a plurality of generally elongate filter tubes mounted therebetween. The filter tubes are constructed of a porous material, such as ceramic, and are suspended in spaced relation one to another within the filter tank from a relatively rigid support member called a "tube sheet". The lower ends of the filter tubes are closed, or capped, such that fluid entering the inlet port of the filter tank must pass through the walls of the filter tubes before reaching the outlet port. Entrained solids within the fluid are thereby deposited on the walls of the filter tubes.
After a period of time, solid material deposited in the form of a cake on the walls of the filter tubes can blind the filter thereby preventing fluid from flowing between the inlet and exit ports of the filter. Accordingly, it becomes necessary to either clean or replace the filter tubes. To facilitate such cleaning or replacement, it is known to construct the filter tubes with an integral upper flange and to suspend the filter tubes within apertures provided in the tube sheet such that the tubes are removable. A gasket disposed between the lip of the flange and the upper surface of the tube sheet prevents leakage of unfiltered fluid from the lower side of the tube sheet to the upper side. To secure the filter tubes to the tube sheet, a bolt and washer arrangement is used for compressing the flange against its respective gasket.
A limitation of the foregoing arrangement for securing the filter tubes to the tube sheet resides in the inability of the bolt and washer to maintain the filter tube in sealed relation to the tube sheet in high temperature applications. For example, high temperature fluids can cause differential expansion between the filter tube flange and tube sheet. The effects of differential expansion are particularly prevalent in filters having filter tubes constructed of a ceramic material, which has a low coefficient of thermal expansion by comparison to a steel tube sheet, for example. In addition, a ceramic filter tube is characteristically brittle, and thus its flange is highly susceptible to fracture when a bolt and washer arrangement is used to secure the flange to the tube sheet.